(1) Field of the Invention
The present invention relates to a combine harvester known as the "straight through" type in which the crop reaped at a reaping section attached to the front of the harvester body is delivered to a threshing chamber for threshing treatment. While the resulting grain is discharged downward from the threshing chamber, straw and part of grain, or tailings, are discharged rearwardly on to oscillatable straw walkers to undergo a separating operation.
(2) Description of the Prior Art
The passage of the crop through a conventional combine harvester is described by reference to FIG. 8 which is a schematic plan view. This type of combine harvester reaps the crop at a reaping section 6' disposed at the front of its body, and collects the reaped crop at a transversely mid-position of the reaping section, from which the crop is delivered by a conveyer 7' to a threshing chamber 8" for threshing treatment. The resulting mixture of straw and grain, or tailings needing further threshing, is passed on to oscillatable straw walkers 13' arranged rearwardly of the threshing chamber 8" to receive a separating treatment. The reaping section 6' includes right and left screw conveyers of opposite threading to collect the reaped crop substantially in a mid-position transversely of the harvester. The purpose of concentrating the reaped crop is to form a bulky heap of the crop to facilitate pickup by the conveyer 7'. The threshing chamber 8" is rather narrow since its transverse dimension L' is determined according to transverse dimension B' of the conveyer 7'. Therefore, the straw walkers 13' too are rather narrow since their transverse dimension A' is determined according to the transverse dimension L' of the threshing chamber 8".
Varied improvements have been made in the prior construction described above in order to achieve higher separating efficiency, and one of them is enlargement of the area of the straw walkers 13'. However, the straw walkers 13' cannot be wide since its transverse dimension A' has to be limited governed by the transverse dimensions L', B' of the threshing chamber 8" and the conveyer 7'. Enlargement of the area of the straw walkers 13' is therefore possible only by elongating them rearwardly, but this has the disadvantage of enlarging the harvester with an increased longitudinal size. Even if the straw walkers 13' are enlarged in the transverse direction, this alone does not lead to improvement in separating efficiency since the threshed product from the narrow threshing chamber 8" does not spread over the whole width of the straw walkers 13'.
Enlarging both the conveyer 7' and the threshing chamber 8" in the transverse direction has the disadvantages of enlarging the conveyer 7' which is necessarily adapted to be vertically oscillatable and of deteriorating the pickup by the conveyer 7' of the crop since the crop has to be less concentrated resulting in a less bulky heap of the crop at the reaping section 6'. It has therefore been desired to improve the selecting efficiency of the straw walkers 13' without increasing the entire length of the combine harvester and while retaining the good pickup by the conveyer 7'.